A thrombus formed in a portion of a vein, for example, may cause pain or swelling, and this may be treated by removing the thrombus with a thrombus-removing device that is percutaneously inserted into the vein. In such a treatment, if the entirety or a portion of the thrombus that has been separated from the wall of the blood vessel is carried by blood flow and reaches the lungs, there is a risk that pulmonary embolism will occur. Therefore, when such a treatment is performed, a thrombolytic agent is used before, during, and/or after the treatment, or the separated thrombus is removed as thoroughly as possible by suction during the treatment. However, even when these processes are carried out, there is still a possibility that a separated thrombus that is dangerously large from a clinical point of view will reach, for example, the lungs.
A filter that collects thrombi that flow through a blood vessel, for example, may be used to avoid pulmonary embolism (see, for example, U.S. Pat. No. 8,562,637). The filter, which has a mesh structure, is inserted into a blood vessel in a contracted state and expanded in the blood vessel.
It is difficult to collect small thrombi with the filter described in U.S. Pat. No. 8,562,637 because the mesh openings widen as the filter expands in the blood vessel. It is also difficult to suck the thrombi collected by the filter because the thrombi need to be sucked against strong blood flow.